Parallel windows and sharing of files

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http://askubuntu.com – Recently I installed parallel windows in my Ubuntu 12.04.1 LTS using virtualbox. But I want to know how to access external hard disks or usb in the virtual windows 7. When I plug in external storage device, only Ubuntu is detecting it. But the virtual windows 7 unable to detect and I can't access it from windows 7. Anyone knows, how to link the files between ubuntu and parallel windows so that files can be shared in each OS at the same time? (HowTos)